Background and aims – We studied a cluster of trees in the Leguminosae subfamily Detarioideae, to: (1) determine the size, structure, and tree species composition of this cluster; (2) map the size, shape, and structure of groups of individual Detarioideae tree species in the cluster; (3) hypothesize on the origin and maintenance of the cluster. 

Location – Lowland rain forest in south Korup National Park, in the Southwest Region of Cameroon.

Material and methods – Trees in permanent plots were recorded using standard plot enumeration techniques. Outside plots, single-species tree groups were recorded by a rapid technique. From this data, detailed maps of groups of trees were prepared.

Key results – Detarioideae tree species occur co-dominant in a cluster of at least 32 km² with an irregular shape. The cluster contained at least 42 Detarioideae tree species; at least 29 of these occurred in groups ranging in size from 50 to 4000 m across, depending on the species. Groups usually had circular shapes, caused by ballistic seed dispersal. Each species was distributed discontinuously within the cluster, and each section of the cluster contained a specific set of Detarioideae species. The percentage of Detarioideae trees ≥ 60 cm stem diameter on 50 ha was up to 76% in Detarioideae-rich forest, to 6% in Detarioideae-poor forest. Of all trees in the centre of the cluster, 97.2% belonged to non-pioneer forest species, which indicates that disturbance levels were low during the past generations of trees.

Conclusions – The forests in the Detarioideae cluster have not been subject to substantial human and natural impacts in historic or prehistoric times. Such forests are exceptional in Africa. Detarioideae clusters may indicate glacial age forest refuges, especially clusters that contain both many different Detarioideae species and some Detarioideae species endemic to the cluster.

The methods used for collection of the data are described in the main paper. They were based on the approaches of:

Newbery, D. M., X. M. van der Burgt, and M. A. Moravie. 2004. Structure and inferred dynamics of a large grove of Microberlinia bisulcata trees in central African rain forest: the possible role of periods of multiple disturbance events. Journal of Tropical Ecology 20:131-143.
Newbery, D. M., X. M. van der Burgt, M. Worbes, and G. B. Chuyong. 2013. Transient dominance in a central African rain forest. Ecological Monographs 83:339-382.

Correction to Newbery et al. (2013). On page 343 of this article, the corner of the P-plot referred to was incorrect: it should read 'southwest' and not 'southeast': The full co-ordinates of the SW corner of the P-plot are, accordingly: UTM 32N, 0476438 E, 0553538 N, 96 m. In decimal degrees: 8.78745°E, 5.00787°N.

Groups of Microberlinia bisulcata
The file ‘Mb_mapped-groups.csv.txt’ contains the 1934 trees of Microberlinia bisulcata ≥ 10 cm stem diameter, recorded in the three known groups (or ‘groves’) in southern Korup. Some trees were located within two permanent plots, and the others were outside of them.
Plot: N = N group; O = O group; PE = P group, extensions to P plot; PNW = P group, NW plot; PG = P group, trees outside plots; PP = P group, P plot.
Long, Lat: Longitude and latitude co-ordinates (WGS84).
Tag: The tag number on the tree. Trees outside plots usually did not have a tag number. [‘NA’ indicates that the tree was not tagged.]
Dm: Stem diameter (cm), At: Height of measurement above ground (m). Date: Date of measurement.
Meth: Method used to measure stem diameter; C, Criterion 400 ranging laser instrument; B,
binocular comparison of stem width against a scale next to tree; R, Bitterlich Spiegel optical relascope; T, girth with steel tape.

Distribution of Tetraberlinia spp.
The file ‘TT_transect_records.csv.txt’ contains 1563 records (Recnr) of the presence (= 1) or absence (= 0) of Tetraberlinia bifoliolata (Tb) and T. korupensis (Tk) trees, in 50-m segments along a set of line transects in southern Korup. Usually TT trees were mature individuals but sometimes they were smaller individuals, even seedlings. Long, Lat: Longitude and latitude coordinates (WGS84). Date: Date of recording.